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			<h1>Python3 数据结构</h1>
<p>本章节我们主要结合前面所学的知识点来介绍Python数据结构。</p>
<hr>
<h2>列表</h2>
<p>Python中列表是可变的，这是它区别于字符串和元组的最重要的特点，一句话概括即：列表可以修改，而字符串和元组不能。
</p>
<p>以下是 Python 中列表的方法：</p>
<table class="reference">
<tr>
<th>方法</th>
<th>描述</th>
</tr>
<tr>
<td>list.append(x)
</td>
<td>把一个元素添加到列表的结尾，相当于 a[len(a):] = [x]。
</td>
</tr>

<tr>
<td>list.extend(L)
</td>
<td>通过添加指定列表的所有元素来扩充列表，相当于 a[len(a):] = L。 
</td>
</tr>

<tr>
<td>list.insert(i, x)
</td>
<td>在指定位置插入一个元素。第一个参数是准备插入到其前面的那个元素的索引，例如 a.insert(0, x) 会插入到整个列表之前，而 a.insert(len(a), x) 相当于 a.append(x) 。
</td>
</tr>
<tr>
<td>list.remove(x)
</td>
<td>删除列表中值为 x 的第一个元素。如果没有这样的元素，就会返回一个错误。
</td>
</tr>

<tr>
<td>list.pop([i])
</td>
<td>从列表的指定位置移除元素，并将其返回。如果没有指定索引，a.pop()返回最后一个元素。元素随即从列表中被移除。（方法中 i 两边的方括号表示这个参数是可选的，而不是要求你输入一对方括号，你会经常在 Python 库参考手册中遇到这样的标记。）
</td>
</tr>

<tr>
<td>list.clear()
</td>
<td>移除列表中的所有项，等于del a[:]。
</td>
</tr>

<tr>
<td>list.index(x)
</td>
<td>返回列表中第一个值为 x 的元素的索引。如果没有匹配的元素就会返回一个错误。
</td>
</tr>

<tr>
<td>list.count(x)
</td>
<td>返回 x 在列表中出现的次数。
</td>
</tr>

<tr>
<td>list.sort()
</td>
<td>对列表中的元素进行排序。
</td>
</tr>

<tr>
<td>list.reverse()
</td>
<td>倒排列表中的元素。
</td>
</tr>

<tr>
<td>list.copy()
</td>
<td>返回列表的浅复制，等于a[:]。
</td>
</tr>
</table>
<p>下面示例演示了列表的大部分方法：</p>

<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> a <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>a.<span style="color: #05a;">count</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">333</span><span style="color: Olive;">&#41;</span><span style="color: Gray;">,</span> a.<span style="color: #05a;">count</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">66.25</span><span style="color: Olive;">&#41;</span><span style="color: Gray;">,</span> a.<span style="color: #05a;">count</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">'x'</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Maroon;">2</span> <span style="color: Maroon;">1</span> <span style="color: Maroon;">0</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">insert</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">1</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">333</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">index</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">333</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Maroon;">1</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">remove</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">333</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">reverse</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">66.25</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a.<span style="color: #05a;">sort</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span>-<span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Olive;">&#93;</span><br />
</div></div>

<p>注意：类似 insert, remove 或 sort 等修改列表的方法没有返回值。</p>
<hr>
<h2>将列表当做堆栈使用</h2>
<p>
列表方法使得列表可以很方便的作为一个堆栈来使用，堆栈作为特定的数据结构，最先进入的元素最后一个被释放（后进先出）。用 append() 方法可以把一个元素添加到堆栈顶。用不指定索引的 pop() 方法可以把一个元素从堆栈顶释放出来。例如： 
</p> 

<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> stack <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">6</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">7</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack.<span style="color: #05a;">pop</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Maroon;">7</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack.<span style="color: #05a;">pop</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Maroon;">6</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack.<span style="color: #05a;">pop</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Maroon;">5</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> stack<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Olive;">&#93;</span><br />
</div></div>

<hr>
<h2>将列表当作队列使用</h2>
<p>也可以把列表当做队列用，只是在队列里第一加入的元素，第一个取出来；但是拿列表用作这样的目的效率不高。在列表的最后添加或者弹出元素速度快，然而在列表里插入或者从头部弹出速度却不快（因为所有其他的元素都得一个一个地移动）。
</p>

<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">from</span> <span style="color: #05a;">collections</span> <span style="color: Green;font-weight:bold;">import</span> deque<br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue <span style="color: Gray;">=</span> deque<span style="color: Olive;">&#40;</span><span style="color: Olive;">&#91;</span><span style="color: #a11;">&quot;Eric&quot;</span><span style="color: Gray;">,</span> <span style="color: #a11;">&quot;John&quot;</span><span style="color: Gray;">,</span> <span style="color: #a11;">&quot;Michael&quot;</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">&quot;Terry&quot;</span><span style="color: Olive;">&#41;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #a50"># Terry arrives</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">&quot;Graham&quot;</span><span style="color: Olive;">&#41;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># Graham arrives</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue.<span style="color: #05a;">popleft</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #a50"># The first to arrive now leaves</span><br />
<span style="color: #a11;">'Eric'</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue.<span style="color: #05a;">popleft</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #a50"># The second to arrive now leaves</span><br />
<span style="color: #a11;">'John'</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> queue &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #a50"># Remaining queue in order of arrival</span><br />
deque<span style="color: Olive;">&#40;</span><span style="color: Olive;">&#91;</span><span style="color: #a11;">'Michael'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'Terry'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'Graham'</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span><br />
</div></div>

<hr>
<h2>列表推导式</h2>
<p>列表推导式提供了从序列创建列表的简单途径。通常应用程序将一些操作应用于某个序列的每个元素，用其获得的结果作为生成新列表的元素，或者根据确定的判定条件创建子序列。 
</p>
<p>
每个列表推导式都在 for 之后跟一个表达式，然后有零到多个 for 或 if 子句。返回结果是一个根据表达从其后的 for 和 if 上下文环境中生成出来的列表。如果希望表达式推导出一个元组，就必须使用括号。

</p>
<p>这里我们将列表中每个数值乘三，获得一个新的列表：</p>

<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> vec <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span>*x <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec<span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Gray;">,</span> <span style="color: Maroon;">18</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<p>现在我们玩一点小花样：</p>
<div class="example"><div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span>x<span style="color: Gray;">,</span> x**<span style="color: Maroon;">2</span><span style="color: Olive;">&#93;</span> <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec<span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">16</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">36</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#93;</span><br />
</div></div>

<p>
这里我们对序列里每一个元素逐个调用某方法：
</p>
<div class="example"><h2 class="example">实例</h2> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> freshfruit <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: #a11;">' &nbsp;banana'</span><span style="color: Gray;">,</span> <span style="color: #a11;">' &nbsp;loganberry '</span><span style="color: Gray;">,</span> <span style="color: #a11;">'passion fruit &nbsp;'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span>weapon.<span style="color: #05a;">strip</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span> <span style="color: Green;font-weight:bold;">for</span> weapon <span style="color: Green;font-weight:bold;">in</span> freshfruit<span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: #a11;">'banana'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'loganberry'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'passion fruit'</span><span style="color: Olive;">&#93;</span><br />
</div></div>

<p>我们可以用 if 子句作为过滤器： </p>

<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span>*x <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec <span style="color: Green;font-weight:bold;">if</span> x <span style="color: Gray;">&gt;</span> <span style="color: Maroon;">3</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">12</span><span style="color: Gray;">,</span> <span style="color: Maroon;">18</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span>*x <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec <span style="color: Green;font-weight:bold;">if</span> x <span style="color: Gray;">&lt;</span> <span style="color: Maroon;">2</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#93;</span><br />
</div></div>

<p>以下是一些关于循环和其它技巧的演示：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> vec1 <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> vec2 <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">3</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">9</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span>x*y <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec1 <span style="color: Green;font-weight:bold;">for</span> y <span style="color: Green;font-weight:bold;">in</span> vec2<span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">18</span><span style="color: Gray;">,</span> <span style="color: Maroon;">16</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">36</span><span style="color: Gray;">,</span> <span style="color: Maroon;">24</span><span style="color: Gray;">,</span> <span style="color: Maroon;">18</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">54</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span>x+y <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> vec1 <span style="color: Green;font-weight:bold;">for</span> y <span style="color: Green;font-weight:bold;">in</span> vec2<span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">7</span><span style="color: Gray;">,</span> <span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Gray;">,</span> <span style="color: Maroon;">9</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">3</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span>vec1<span style="color: Olive;">&#91;</span>i<span style="color: Olive;">&#93;</span>*vec2<span style="color: Olive;">&#91;</span>i<span style="color: Olive;">&#93;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Teal;">len</span><span style="color: Olive;">&#40;</span>vec1<span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Gray;">,</span> -<span style="color: Maroon;">54</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<p>列表推导式可以使用复杂表达式或嵌套函数：
</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Teal;">str</span><span style="color: Olive;">&#40;</span><span style="color: Teal;">round</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">355</span>/<span style="color: Maroon;">113</span><span style="color: Gray;">,</span> i<span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: #a11;">'3.1'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'3.14'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'3.142'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'3.1416'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'3.14159'</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<hr>
<h2>嵌套列表解析</h2>
<p>
Python的列表还可以嵌套。
</p>
<p>以下实例展示了3X4的矩阵列表：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> matrix <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><br />
... &nbsp; &nbsp; <span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span><br />
... &nbsp; &nbsp; <span style="color: Olive;">&#91;</span><span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Gray;">,</span> <span style="color: Maroon;">8</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span><br />
... &nbsp; &nbsp; <span style="color: Olive;">&#91;</span><span style="color: Maroon;">9</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Gray;">,</span> <span style="color: Maroon;">11</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span><br />
... <span style="color: Olive;">&#93;</span><br />
</div></div>
<p>以下实例将3X4的矩阵列表转换为4X3列表：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span>row<span style="color: Olive;">&#91;</span>i<span style="color: Olive;">&#93;</span> <span style="color: Green;font-weight:bold;">for</span> row <span style="color: Green;font-weight:bold;">in</span> matrix<span style="color: Olive;">&#93;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">4</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">9</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Gray;">,</span> <span style="color: Maroon;">11</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<p>以下实例也可以使用以下方法来实现：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> transposed <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">4</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: #05a;">transposed</span>.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#91;</span>row<span style="color: Olive;">&#91;</span>i<span style="color: Olive;">&#93;</span> <span style="color: Green;font-weight:bold;">for</span> row <span style="color: Green;font-weight:bold;">in</span> matrix<span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: Gray;">&gt;&gt;&gt;</span> transposed<br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">9</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Gray;">,</span> <span style="color: Maroon;">11</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<p>另外一种实现方法：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> transposed <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">4</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: #a50"># the following 3 lines implement the nested listcomp</span><br />
... &nbsp; &nbsp; <span style="color: #05a;">transposed_row</span> <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: Olive;">&#93;</span><br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">for</span> row <span style="color: Green;font-weight:bold;">in</span> matrix:<br />
... &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #05a;">transposed_row</span>.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span>row<span style="color: Olive;">&#91;</span>i<span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span><br />
... &nbsp; &nbsp; <span style="color: #05a;">transposed</span>.<span style="color: #05a;">append</span><span style="color: Olive;">&#40;</span>transposed_row<span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: Gray;">&gt;&gt;&gt;</span> transposed<br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Gray;">,</span> <span style="color: Maroon;">9</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">7</span><span style="color: Gray;">,</span> <span style="color: Maroon;">11</span><span style="color: Olive;">&#93;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#91;</span><span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">8</span><span style="color: Gray;">,</span> <span style="color: Maroon;">12</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<hr>
<h2>del 语句</h2>
<p>
使用 del 语句可以从一个列表中根据索引来删除一个元素，而不是值来删除元素。这与使用 pop() 返回一个值不同。可以用 del 语句从列表中删除一个切割，或清空整个列表（我们以前介绍的方法是给该切割赋一个空列表）。例如：
</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> a <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span>-<span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">del</span> a<span style="color: Olive;">&#91;</span><span style="color: Maroon;">0</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">333</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">del</span> a<span style="color: Olive;">&#91;</span><span style="color: Maroon;">2</span>:<span style="color: Maroon;">4</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">66.25</span><span style="color: Gray;">,</span> <span style="color: Maroon;">1234.5</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">del</span> a<span style="color: Olive;">&#91;</span>:<span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#91;</span><span style="color: Olive;">&#93;</span><br />
</div></div>
<p>也可以用 del 删除实体变量： </p>
<pre>
&gt;&gt;&gt; del a
</pre>
<hr>
<h2> 元组和序列 </h2>
<p>
元组由若干逗号分隔的值组成，例如：
</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> t <span style="color: Gray;">=</span> <span style="color: Maroon;">12345</span><span style="color: Gray;">,</span> <span style="color: Maroon;">54321</span><span style="color: Gray;">,</span> <span style="color: #a11;">'hello!'</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> t<span style="color: Olive;">&#91;</span><span style="color: Maroon;">0</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Maroon;">12345</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> t<br />
<span style="color: Olive;">&#40;</span><span style="color: Maroon;">12345</span><span style="color: Gray;">,</span> <span style="color: Maroon;">54321</span><span style="color: Gray;">,</span> <span style="color: #a11;">'hello!'</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a50"># Tuples may be nested:</span><br />
... <span style="color: #05a;">u</span> <span style="color: Gray;">=</span> t<span style="color: Gray;">,</span> <span style="color: Olive;">&#40;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> u<br />
<span style="color: Olive;">&#40;</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">12345</span><span style="color: Gray;">,</span> <span style="color: Maroon;">54321</span><span style="color: Gray;">,</span> <span style="color: #a11;">'hello!'</span><span style="color: Olive;">&#41;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#40;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">3</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">5</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><br />
</div></div>
<p>如你所见，元组在输出时总是有括号的，以便于正确表达嵌套结构。在输入时可能有或没有括号， 不过括号通常是必须的（如果元组是更大的表达式的一部分）。
</p>
<hr>
<h2>集合</h2>
<p>集合是一个无序不重复元素的集。基本功能包括关系测试和消除重复元素。</p>
<p>可以用大括号({})创建集合。注意：如果要创建一个空集合，你必须用 set() 而不是 {} ；后者创建一个空的字典，下一节我们会介绍这个数据结构。</p>
<p>以下是一个简单的演示：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> basket <span style="color: Gray;">=</span> <span style="color: Olive;">&#123;</span><span style="color: #a11;">'apple'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'orange'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'apple'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'pear'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'orange'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'banana'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>basket<span style="color: Olive;">&#41;</span> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># 删除重复的</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'orange'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'banana'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'pear'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'apple'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a11;">'orange'</span> <span style="color: Green;font-weight:bold;">in</span> basket &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span style="color: #a50"># 检测成员</span><br />
<span style="color: Teal;">True</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a11;">'crabgrass'</span> <span style="color: Green;font-weight:bold;">in</span> basket<br />
<span style="color: Teal;">False</span><br />
<br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a50"># 以下演示了两个集合的操作</span><br />
...<br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a <span style="color: Gray;">=</span> <span style="color: Teal;">set</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">'abracadabra'</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> b <span style="color: Gray;">=</span> <span style="color: Teal;">set</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">'alacazam'</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># a 中唯一的字母</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'a'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'r'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'b'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'c'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'d'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a - b &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># 在 a 中的字母，但不在 b 中</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'r'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'d'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'b'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a | b &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># 在 a 或 b 中的字母</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'a'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'c'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'r'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'d'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'b'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'m'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'z'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'l'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a &amp; b &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># 在 a 和 b 中都有的字母</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'a'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'c'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a ^ b &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span style="color: #a50"># 在 a 或 b 中的字母，但不同时在 a 和 b 中</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'r'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'d'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'b'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'m'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'z'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'l'</span><span style="color: Olive;">&#125;</span><br />
</div></div>
<p>集合也支持推导式：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> a <span style="color: Gray;">=</span> <span style="color: Olive;">&#123;</span>x <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> <span style="color: #a11;">'abracadabra'</span> <span style="color: Green;font-weight:bold;">if</span> x <span style="color: Green;font-weight:bold;">not</span> <span style="color: Green;font-weight:bold;">in</span> <span style="color: #a11;">'abc'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> a<br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'r'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'d'</span><span style="color: Olive;">&#125;</span><br />
</div></div>
<hr>
<h2>字典</h2>
<p>另一个非常有用的 Python 内建数据类型是字典。</p>
<p>序列是以连续的整数为索引，与此不同的是，字典以关键字为索引，关键字可以是任意不可变类型，通常用字符串或数值。</p>
<p>理解字典的最佳方式是把它看做无序的键=>值对集合。在同一个字典之内，关键字必须是互不相同。</p>
<p>一对大括号创建一个空的字典：{}。</p>
<p>这是一个字典运用的简单例子： </p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> tel <span style="color: Gray;">=</span> <span style="color: Olive;">&#123;</span><span style="color: #a11;">'jack'</span>: <span style="color: Maroon;">4098</span><span style="color: Gray;">,</span> <span style="color: #a11;">'sape'</span>: <span style="color: Maroon;">4139</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> tel<span style="color: Olive;">&#91;</span><span style="color: #a11;">'guido'</span><span style="color: Olive;">&#93;</span> <span style="color: Gray;">=</span> <span style="color: Maroon;">4127</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> tel<br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'sape'</span>: <span style="color: Maroon;">4139</span><span style="color: Gray;">,</span> <span style="color: #a11;">'guido'</span>: <span style="color: Maroon;">4127</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span>: <span style="color: Maroon;">4098</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> tel<span style="color: Olive;">&#91;</span><span style="color: #a11;">'jack'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Maroon;">4098</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">del</span> tel<span style="color: Olive;">&#91;</span><span style="color: #a11;">'sape'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> tel<span style="color: Olive;">&#91;</span><span style="color: #a11;">'irv'</span><span style="color: Olive;">&#93;</span> <span style="color: Gray;">=</span> <span style="color: Maroon;">4127</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> tel<br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'guido'</span>: <span style="color: Maroon;">4127</span><span style="color: Gray;">,</span> <span style="color: #a11;">'irv'</span>: <span style="color: Maroon;">4127</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span>: <span style="color: Maroon;">4098</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Teal;">list</span><span style="color: Olive;">&#40;</span>tel.<span style="color: #05a;">keys</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: #a11;">'irv'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'guido'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Teal;">sorted</span><span style="color: Olive;">&#40;</span>tel.<span style="color: #05a;">keys</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Olive;">&#91;</span><span style="color: #a11;">'guido'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'irv'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a11;">'guido'</span> <span style="color: Green;font-weight:bold;">in</span> tel<br />
<span style="color: Teal;">True</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: #a11;">'jack'</span> <span style="color: Green;font-weight:bold;">not</span> <span style="color: Green;font-weight:bold;">in</span> tel<br />
<span style="color: Teal;">False</span><br />
</div></div>
<p>构造函数 dict() 直接从键值对元组列表中构建字典。如果有固定的模式，列表推导式指定特定的键值对：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Teal;">dict</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#91;</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">'sape'</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4139</span><span style="color: Olive;">&#41;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#40;</span><span style="color: #a11;">'guido'</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4127</span><span style="color: Olive;">&#41;</span><span style="color: Gray;">,</span> <span style="color: Olive;">&#40;</span><span style="color: #a11;">'jack'</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4098</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'sape'</span>: <span style="color: Maroon;">4139</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span>: <span style="color: Maroon;">4098</span><span style="color: Gray;">,</span> <span style="color: #a11;">'guido'</span>: <span style="color: Maroon;">4127</span><span style="color: Olive;">&#125;</span><br />
</div></div>
<p>此外，字典推导可以用来创建任意键和值的表达式词典：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Olive;">&#123;</span>x: x**<span style="color: Maroon;">2</span> <span style="color: Green;font-weight:bold;">for</span> x <span style="color: Green;font-weight:bold;">in</span> <span style="color: Olive;">&#40;</span><span style="color: Maroon;">2</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Olive;">&#123;</span><span style="color: Maroon;">2</span>: <span style="color: Maroon;">4</span><span style="color: Gray;">,</span> <span style="color: Maroon;">4</span>: <span style="color: Maroon;">16</span><span style="color: Gray;">,</span> <span style="color: Maroon;">6</span>: <span style="color: Maroon;">36</span><span style="color: Olive;">&#125;</span><br />
</div></div>
<p>如果关键字只是简单的字符串，使用关键字参数指定键值对有时候更方便： </p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Teal;">dict</span><span style="color: Olive;">&#40;</span>sape<span style="color: Gray;">=</span><span style="color: Maroon;">4139</span><span style="color: Gray;">,</span> guido<span style="color: Gray;">=</span><span style="color: Maroon;">4127</span><span style="color: Gray;">,</span> jack<span style="color: Gray;">=</span><span style="color: Maroon;">4098</span><span style="color: Olive;">&#41;</span><br />
<span style="color: Olive;">&#123;</span><span style="color: #a11;">'sape'</span>: <span style="color: Maroon;">4139</span><span style="color: Gray;">,</span> <span style="color: #a11;">'jack'</span>: <span style="color: Maroon;">4098</span><span style="color: Gray;">,</span> <span style="color: #a11;">'guido'</span>: <span style="color: Maroon;">4127</span><span style="color: Olive;">&#125;</span><br />
</div></div>
<hr>
<h2>遍历技巧</h2>
<p>
在字典中遍历时，关键字和对应的值可以使用 items() 方法同时解读出来：
</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> knights <span style="color: Gray;">=</span> <span style="color: Olive;">&#123;</span><span style="color: #a11;">'gallahad'</span>: <span style="color: #a11;">'the pure'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'robin'</span>: <span style="color: #a11;">'the brave'</span><span style="color: Olive;">&#125;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> k<span style="color: Gray;">,</span> v <span style="color: Green;font-weight:bold;">in</span> knights.<span style="color: #05a;">items</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>k<span style="color: Gray;">,</span> v<span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: #05a;">gallahad</span> the pure<br />
robin the brave<br />
</div></div>
<p>在序列中遍历时，索引位置和对应值可以使用 enumerate() 函数同时得到：</p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> i<span style="color: Gray;">,</span> v <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">enumerate</span><span style="color: Olive;">&#40;</span><span style="color: Olive;">&#91;</span><span style="color: #a11;">'tic'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'tac'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'toe'</span><span style="color: Olive;">&#93;</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>i<span style="color: Gray;">,</span> v<span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: Maroon;">0</span> tic<br />
<span style="color: Maroon;">1</span> tac<br />
<span style="color: Maroon;">2</span> toe<br />
</div></div>
<p>同时遍历两个或更多的序列，可以使用 zip() 组合： </p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> questions <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: #a11;">'name'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'quest'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'favorite color'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> answers <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: #a11;">'lancelot'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'the holy grail'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'blue'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> q<span style="color: Gray;">,</span> a <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">zip</span><span style="color: Olive;">&#40;</span>questions<span style="color: Gray;">,</span> answers<span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span><span style="color: #a11;">'What is your {0}? &nbsp;It is {1}.'</span>.<span style="color: #05a;">format</span><span style="color: Olive;">&#40;</span>q<span style="color: Gray;">,</span> a<span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: #05a;">What</span> <span style="color: Green;font-weight:bold;">is</span> your name? &nbsp;It <span style="color: Green;font-weight:bold;">is</span> lancelot.<br />
<span style="color: #05a;">What</span> <span style="color: Green;font-weight:bold;">is</span> your quest? &nbsp;It <span style="color: Green;font-weight:bold;">is</span> the holy grail.<br />
<span style="color: #05a;">What</span> <span style="color: Green;font-weight:bold;">is</span> your favorite color? &nbsp;It <span style="color: Green;font-weight:bold;">is</span> blue.<br />
</div></div>
<p>要反向遍历一个序列，首先指定这个序列，然后调用 reversed() 函数： </p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> i <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">reversed</span><span style="color: Olive;">&#40;</span><span style="color: Teal;">range</span><span style="color: Olive;">&#40;</span><span style="color: Maroon;">1</span><span style="color: Gray;">,</span> <span style="color: Maroon;">10</span><span style="color: Gray;">,</span> <span style="color: Maroon;">2</span><span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>i<span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: Maroon;">9</span><br />
<span style="color: Maroon;">7</span><br />
<span style="color: Maroon;">5</span><br />
<span style="color: Maroon;">3</span><br />
<span style="color: Maroon;">1</span><br />
</div></div>
<p>要按顺序遍历一个序列，使用 sorted() 函数返回一个已排序的序列，并不修改原值： </p>
<div class="example"> <div class="example_code">
<span style="color: Gray;">&gt;&gt;&gt;</span> basket <span style="color: Gray;">=</span> <span style="color: Olive;">&#91;</span><span style="color: #a11;">'apple'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'orange'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'apple'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'pear'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'orange'</span><span style="color: Gray;">,</span> <span style="color: #a11;">'banana'</span><span style="color: Olive;">&#93;</span><br />
<span style="color: Gray;">&gt;&gt;&gt;</span> <span style="color: Green;font-weight:bold;">for</span> f <span style="color: Green;font-weight:bold;">in</span> <span style="color: Teal;">sorted</span><span style="color: Olive;">&#40;</span><span style="color: Teal;">set</span><span style="color: Olive;">&#40;</span>basket<span style="color: Olive;">&#41;</span><span style="color: Olive;">&#41;</span>:<br />
... &nbsp; &nbsp; <span style="color: Green;font-weight:bold;">print</span><span style="color: Olive;">&#40;</span>f<span style="color: Olive;">&#41;</span><br />
...<br />
<span style="color: #05a;">apple</span><br />
banana<br />
orange<br />
pear<br />
</div></div>
<hr><h2>参阅文档</h2>
<ul>
<li><a target="_blank" href="../python3/python3-list.html" rel="noopener noreferrer">Python3 列表</a></li>
<li><a target="_blank" href="../python3/python3-tuple.html" rel="noopener noreferrer">Python3 元组</a></li>
<li><a target="_blank" href="../python3/python3-dictionary.html" rel="noopener noreferrer">Python3 字典</a></li>
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<div id="postcomments"  style="display:none;" >
	<ol class="commentlist">
		<li class="comment even thread-even depth-1" id="comment-13203"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;reinhard</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;mrl***xz@hotmail.com</p></div><div id="runoobvote-id-13203" data-commid = "13203" class="upvotejs"><a class="upvote"></a> <span class="count">53</span></div></div><div class="comt-main" id="div-comment-13203"><p>元组不可变，若元组的成员可变类型，则成员可编辑。
</p><pre>
a = [1,2,3,4]
b = [5,6,7,8]
c = [9,10,11,12]
t = a,b,c
print(t)
del b[1:4]
print(t)
</pre>
<p>
输出：
</p><pre>
([1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12])
([1, 2, 3, 4], [5], [9, 10, 11, 12])</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">reinhard</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;reinhard</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;mrl***xz@hotmail.com</p></div></span>6年前 (2017-06-21)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-15802"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;。。。</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;928***428@qq.com</p></div><div id="runoobvote-id-15802" data-commid = "15802" class="upvotejs"><a class="upvote"></a> <span class="count">166</span></div></div><div class="comt-main" id="div-comment-15802">
<p data-title="Python 列表推导式">列表推导式（又称列表解析式）提供了一种简明扼要的方法来创建列表。</p>
<p>它的结构是在一个中括号里包含一个表达式，然后是一个for语句，然后是 0 个或多个 for 或者 if 语句。那个表达式可以是任意的，意思是你可以在列表中放入任意类型的对象。返回结果将是一个新的列表，在这个以 if 和 for 语句为上下文的表达式运行完成之后产生。</p>
<p>列表推导式的执行顺序：各语句之间是嵌套关系，左边第二个语句是最外层，依次往右进一层，左边第一条语句是最后一层。</p>
<pre>[x*y for x in range(1,5) if x &gt; 2 for y in range(1,4) if y &lt; 3]</pre>
<p>他的执行顺序是:</p>
<pre>for x in range(1,5)
    if x &gt; 2
        for y in range(1,4)
            if y &lt; 3
                x*y</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="../note/15802">。。。</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;。。。</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;928***428@qq.com</p></div></span>6年前 (2017-08-03)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-17452"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;小盟主</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;165***0317@qq.com</p></div><div id="runoobvote-id-17452" data-commid = "17452" class="upvotejs"><a class="upvote"></a> <span class="count">66</span></div></div><div class="comt-main" id="div-comment-17452"><p>有多个列表需要遍历时，需要zip，除了用'{0}{1}'.format(q,a)的方法，还可以使用%s方法（两者效果一样一样的）：</p>
<pre>questions=['name','quest','favorite color']
answers=['qinshihuang','the holy','blue']
for q,a in zip(questions,answers):
    print('what is your %s? it is %s' %(q,a))
    print('what is your {0}? it is {1}'.format(q,a))</pre>
<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">小盟主</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;小盟主</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;165***0317@qq.com</p></div></span>6年前 (2017-09-13)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-42044"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;空白runoob</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;tia***i2nd@163.com</p></div><div id="runoobvote-id-42044" data-commid = "42044" class="upvotejs"><a class="upvote"></a> <span class="count">62</span></div></div><div class="comt-main" id="div-comment-42044"><p>教程中遍历 dict 使用的 .items() 方法配合 for 循环，非常简明易懂，但有一项需要注意的是，在 for 循环中，使用单个变量和双变量的区别，注意观察以下两个例子的区别：</p>

<pre>&gt;&gt;&gt; knights = {'gallahad': 'the pure', 'robin': 'the brave'}
&gt;&gt;&gt; for k, v in knights.items():
...     print(k, v)
...
gallahad the pure
robin the brave</pre>

<p>===========================分隔线===========================</p>

<pre>&gt;&gt;&gt; knights = {'gallahad': 'the pure', 'robin': 'the brave'}
&gt;&gt;&gt; for k in knights.items():
...     print(k)
...
('gallahad', 'the pure')
('robin', 'the brave')</pre>

<p>使用 k 和 v 两个变量时，将键与值分别赋予 k 和 v。使用 k 一个变量时，将对应的键与值作为一个整体赋给 k。所以，最终 print 的显示内容是有区别的。不只是此例，程序设计过程中有很多地方都会体现个体与整体的差异，虽然显示出来的结果非常相似，但逻辑上却是完全不同的。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">空白runoob</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;空白runoob</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;tia***i2nd@163.com</p></div></span>4年前 (2019-04-19)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-45746"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Cxj</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;150***6419@qq.com</p></div><div id="runoobvote-id-45746" data-commid = "45746" class="upvotejs"><a class="upvote"></a> <span class="count">70</span></div></div><div class="comt-main" id="div-comment-45746"><p>针对上述所讲的的执行顺序介绍，讲解一下正文中的一个例子：</p>

<pre>&gt;&gt;&gt; matrix = [
...     [1, 2, 3, 4],
...     [5, 6, 7, 8],
...     [9, 10, 11, 12],
... ]</pre>
<p>以下实例将 3X4 的矩阵列表转换为 4X3 列表：</p>
<pre>&gt;&gt;&gt; [[row[i] for row in matrix] for i in range(4)]
[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]</pre>
<p>这个例子中的执行顺序应该为：</p>

<pre>for i in range(4)
    for row in matrix
        row[i]</pre>

<p>即将每一个 matrix 中的列表元素的第一个放在一起、第二个放在一起、第三个放在一起、第四个元素放在一起作为一个新的列表元素。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Cxj</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Cxj</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;150***6419@qq.com</p></div></span>4年前 (2019-08-14)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-46522"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;小闪闪</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;517***504@qq.com</p></div><div id="runoobvote-id-46522" data-commid = "46522" class="upvotejs"><a class="upvote"></a> <span class="count">60</span></div></div><div class="comt-main" id="div-comment-46522"><p>使用小括号包裹推导式会生成生成器对象，而不是元组。</p>

<pre>&gt;&gt;&gt; a = (2*x for x in range(2))
&gt;&gt;&gt; type(a)
&lt;class 'generator'&gt;
&gt;&gt;&gt; next(a)
0
&gt;&gt;&gt; next(a)
2
&gt;&gt;&gt; next(a)
Traceback (most recent call last):
  File "&lt;pyshell#691&gt;", line 1, in &lt;module&gt;
    next(a)
StopIteration</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">小闪闪</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;小闪闪</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;517***504@qq.com</p></div></span>4年前 (2019-09-06)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-54067"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;higandown</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;hig***own@qq.com</p></div><div id="runoobvote-id-54067" data-commid = "54067" class="upvotejs"><a class="upvote"></a> <span class="count">20</span></div></div><div class="comt-main" id="div-comment-54067"><p>推导式不仅还能加人三元表达式进行一些更加复杂的多层判断:</p>

<pre>array = []
for i in range(30):
    if i%3==0 and i%5==0:
        array.append("能被3-5整除")
    elif i%5==0:
        array.append("能被5整除")
    elif i%3==0:
        array.append("能被3整除")
    else:
        array.append("不能能被3-5整除")

array = ["能被3-5整除" if i%3==0 and i%5==0 else "能被5整除" if i%5==0 else "能被3整除" if i%3==0 else "不能被3-5整除" for i in range(30)]
print(array)</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">higandown</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;higandown</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;hig***own@qq.com</p></div></span>3年前 (2020-05-29)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-57280"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Indecision</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;153***5993@qq.com</p></div><div id="runoobvote-id-57280" data-commid = "57280" class="upvotejs"><a class="upvote"></a> <span class="count">30</span></div></div><div class="comt-main" id="div-comment-57280"><p>针对上述所讲的的执行顺序介绍，讲解一下正文中的一个例子：</p>

<pre>matrix = [ [7, 2, 9, 4], [5, 6, 9, 8], [9, 10, 11, 12],]


relist1 = [row[i] for i in range(4) for row in matrix]
relist2 = [[row[i] for row in matrix] for i in range(4)]

print(relist1)
print(relist2)</pre>

<p>输出：</p>
<pre>[7, 5, 9, 2, 6, 10, 9, 9, 11, 4, 8, 12]
[[7, 5, 9], [2, 6, 10], [9, 9, 11], [4, 8, 12]]</pre>
<p>relist1 返回为一个单层列表。</p><p>

relist2。内部循环结果先生成一个列表，并以子列表的形式添加到外层列表中。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Indecision</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Indecision</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;153***5993@qq.com</p></div></span>3年前 (2020-09-24)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-65811"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;於黾</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;252***70@qq.com</p></div><div id="runoobvote-id-65811" data-commid = "65811" class="upvotejs"><a class="upvote"></a> <span class="count">85</span></div></div><div class="comt-main" id="div-comment-65811"><p>楼上很多人都在讨论推导式，这个东西在我看来是可有可无的，除了节省代码之外没什么用处，反而影响可读性（对于新手会不友好）</p>
<p>
反而是另一个问题值得详细的说明：<strong>元组的装包与拆包</strong></p>

<p>先看下面的代码：</p>

<pre>a=1
b=2
a,b=b,a
print(a,b)</pre><p>
我们都知道这样可以很方便的对2个值进行互换，然而这个操作其实涉及到元组的装包与拆包</p>
<p>
完全的写法应该是下面这样的：</p>

<pre>(a,b)=(b,a)</pre><p>
将a和b放入一个元组中，然后通过元组赋值</p><p>

但是python会自动进行元组的装包与拆包操作，因此下面2个式子与上面是等价的：</p>
<pre>
a,b=(b,a)
(a,b)=b,a</pre><p>
理解了元组的自动装包拆包，再回头看函数的返回值，就可以更深入的理解了</p>
<p>
函数其实并不能返回多个值，只能返回一个值。</p><p>

当有多个返回值时，其实是自动将他们放入一个元组中，然后返回这个元组</p>

<pre>def f():
  return 1,2,3

print(f())</pre><p>
此时函数返回值其实是（1,2,3），是个元组</p>
<p>
但是当我们用3个变量同时去接收这个返回值时</p>
<pre>
a,b,c=f()</pre>
<p>相当于</p>

<pre>a,b,c=(1,2,3)</pre><p>
由于元组自动拆包，造成a=1,b=2,c=3，看似返回了多个值一样</p><p>

如果不理解这一点，就会搞不清为什么有时候就有括号，有时候就没括号</p><p>

关键有括号和没括号类型完全不一样，搞混了可是不行的</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">於黾</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;於黾</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;252***70@qq.com</p></div></span>2年前 (2021-08-06)</div></div></li><!-- #comment-## -->
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